Search Space Monitoring

ABSTRACT

There are provided mechanisms for monitoring search spaces. A first method performed by a wireless device comprises receiving an Orthogonal Frequency-Division Multiplexing (OFDM) symbol in a downlink slot. At least part of the OFDM symbol is included in a device-specific search space and in a common search space. The first method comprises monitoring the device-specific search space for at least one device-specific reference signal (RS) and monitoring the common search space for at least one non-device-specific RS. In a second method, a radio access network node transmits an OFDM symbol included in a device-specific search space and in a common search space. The device-specific search space contains a device-specific RS, or the non-device specific search space contains a non-device-specific RS, or both of these apply.

TECHNICAL FIELD

Embodiments presented herein relate to a method, a wireless device, acomputer program, and a computer program product for monitoring searchspaces.

BACKGROUND

In communications networks, there may be a challenge to obtain goodperformance and capacity for a given communications protocol, itsvarious design aspects and the physical environment in which thecommunications network is deployed.

For example, one design aspect with a considerable impact on performanceand capacity for a given communications protocol in a communicationsnetwork is the use of reference signals (RSs). RSs of different typescan be transmitted, received, and used within an orthogonalfrequency-division multiplexing (OFDM) symbol.

In addition to RSs, there are basically two types of physical downlinkcontrol channels (PDCCHs) envisioned for future radio accesstechnologies; common PDCCHs and device-specific PDCCHs. The PDCCHs maybe transmitted in a common control region or a device-specific controlregion.

In the 3GPP Long Term Evolution (LTE) suite of telecommunicationstandards, a search space may be understood as a set of candidatecontrol channels which a wireless device is supposed to attempt todecode. There may be more than one search space. In particular, a searchspace may be a common search space, which is common to all wirelessdevice of the cell, or a device-specific search space, which may haveproperties determined by a non-injective function of device identity andmay thus be shared with some other devices of the cell. In a LTE cell,all search spaces may be contained in a constant set of one or moresubbands.

For the PDCCH in 3GPP Rel. 8, the common control region (structured as acommon control search space) is located within the protocollayer-1/layer-2 (L1/L2) control regions in the first few OFDM symbolsspanning the entire system bandwidth, as well as any device-specificcontrol regions (structured as device-specific search space(s)). Inaddition, common reference signals (CRS) are transmitted in the entiresubframe (including the L1/L2 control region). Any PDCCH in the commonor device-specific search space(s) are transmitted using the sameantenna weights (beamforming) as the CRS.

The wireless device monitors the common and the device-specific searchspaces in respective control regions and uses the CRS to estimate achannel, in order to do blind decoding of possible PDCCH candidates inthe search spaces. This prevents device-specific beamforming of anydevice-specific PDCCHs, since the CRSs are not assumed to be beamformedin a device-specific way. Many of the PDCCH messages are not addressedto individual wireless devices but to a group of wireless devices, forexample, random access responses, system information, allocation andpaging information.

In 3GPP Rel. 11, a new set of device-specific control channel searchspace(s) were added along with related device-specific demodulationreference signals (DMRS). This enables the network to senddevice-specific control messages to a wireless device usingdevice-specific beamforming, for example directed towards a certainwireless device or a certain group of wireless devices. Search spacesknown as ePDCCH search spaces (where the prefix e- is short forenhanced) are located in a control region sent (and received) after theL1/L2 symbols in the data region, and are confined to a small subset ofresource blocks.

FIG. 1 schematically illustrates an example of a structure of a 3GPPRel. 11 subframe 150 showing frequency usage (in terms of bandwidth) asa function of time. The subframe 150 comprises a PDCCH control region190, a data region 170 and an ePDCCH control region 180, where theePDCCH control region 180 comprises an ePDCCH 160. The ePDCCH 160 maycarry control information scheduling a data region 170 in the samesubframe. The wireless device monitors the ePDCCH in the one or moreePDCCH search spaces 180. If an ePDCCH 160 is found, the found ePDCCHmay identify a data region 170 in the subframe. It follows from FIG. 1that the decoding of any data in the scheduled data region cannot bestarted until the ePDCCH region has been fully monitored, that is, afterthe entire subframe has been received. There may as well bedeinterleaving.

Hence, there is a need for an improved monitoring in search spaces.

SUMMARY

An object of embodiments herein is to provide efficient monitoring ofsearch spaces.

According to a first aspect there is presented a method for monitoringsearch spaces. The method is performed by a wireless device. The methodcomprises receiving an OFDM symbol in a downlink slot. At least part ofthe OFDM symbol is included in a device-specific search space and in acommon search space. The method comprises monitoring the device-specificsearch space for at least one device-specific reference signal. Themethod comprises monitoring the common search space for at least onenon-device-specific reference signal.

Advantageously this method provides efficient monitoring of the searchspaces, in turn enabling efficient monitoring of control regions.

Advantageously this method for monitoring search spaces reduces latencycompared to existing mechanisms for monitoring of control regions.Decoding may start after reception of the control symbol and the firstdata symbol, instead of at the end of the entire subframe as in existingmechanisms for monitoring of control regions. This latency gain may bepossible regardless of whether the control data is common ordevice-specific.

According to a second aspect there is presented a wireless device formonitoring search spaces. The wireless device comprises processingcircuitry and a communications interface. The processing circuitry isconfigured to cause the wireless device to receive an OFDM symbol in adownlink slot using the communications interface. At least part of theOFDM symbol is included in a device-specific search space and in acommon search space. The processing circuitry is configured to cause thewireless device to monitor the device-specific search space for at leastone device-specific reference signal. The processing circuitry isconfigured to cause the wireless device to monitor the common searchspace for at least one non-device-specific reference signal.

According to a third aspect there is presented a wireless device formonitoring search spaces. The wireless device comprises processingcircuitry, a communications interface, and storage medium. The storagemedium stores instructions that, when executed by the processingcircuitry, cause the wireless device to perform operations, or steps.The operations, or steps, cause the wireless device to receive an OFDMsymbol in a downlink slot using the communications interface. At leastpart of the OFDM symbol is included in a device-specific search spaceand in a common search space. The operations, or steps, cause thewireless device to monitor the device-specific search space for at leastone device-specific reference signal. The operations, or steps, causethe wireless device to monitor the common search space for at least onenon-device-specific reference signal.

According to a fourth aspect there is presented a wireless device formonitoring search spaces. The wireless device comprises a receive moduleconfigured to receive an OFDM symbol in a downlink slot. At least partof the OFDM symbol is included in a device-specific search space and ina common search space. The wireless device comprises a monitor moduleconfigured to monitor a device-specific search space using the at leastone device-specific reference signal. The wireless device comprises amonitor module configured to monitor a common search space using the atleast one non-device-specific reference signal.

According to a fifth aspect there is presented a computer program formonitoring search spaces, the computer program comprising computerprogram code which, when run on a wireless device, causes the wirelessdevice to perform a method according to the first aspect.

According to a sixth aspect there is presented a computer programproduct comprising a computer program according to the fifth aspect anda computer readable storage medium on which the computer program isstored. The computer readable storage medium may be a non-transitorycomputer readable storage medium.

According to a seventh aspect there is presented a method for enablingmonitoring of search spaces, in particular enabling a wireless device'smonitoring of search spaces. The method is performed by a radio accessnetwork node. The method comprises transmitting an OFDM symbol in adownlink slot. At least part of the OFDM symbol is included in adevice-specific search space and a common reference search space. Thedevice-specific search space comprises a device-specific referencesignal, and/or the common search space comprises a non-device-specificreference signal.

According to an eighth aspect there is presented a radio access networknode for enabling monitoring of search spaces. The radio access networknode comprises processing circuitry and a communication interface. Theprocessing circuitry is configured to cause the radio access networknode to transmit an OFDM symbol in a downlink slot using thecommunications interface. At least part of the OFDM symbol is includedin a device-specific search space and a common reference search space.The device-specific search space comprises a device-specific referencesignal, and/or the common search space comprises a non-device-specificreference signal.

According to a ninth aspect there is presented a radio access networknode for enabling monitoring of search spaces. The radio access networknode comprises processing circuitry, a communication interface, and astorage medium. The storage medium stores instructions that, whenexecuted by the processing circuitry, cause the radio access networknode to transmit an OFDM symbol in a downlink slot using thecommunications interface. At least part of the OFDM symbol is includedin a device-specific search space and a common reference search space.The device-specific search space comprises a device-specific referencesignal, and/or the common search space comprises a non-device-specificreference signal.

According to a tenth aspect there is presented a radio access networknode for enabling monitoring of search spaces. The radio access networknode comprises a transmit module configured to transmit an OFDM symbolin a downlink slot. At least part of the OFDM symbol is included in adevice-specific search space and a common reference search space. Thedevice-specific search space comprises a device-specific referencesignal, and/or the common search space comprises a non-device-specificreference signal.

According to an eleventh aspect there is presented a computer programfor enabling monitoring of search spaces, the computer programcomprising computer program code which, when run on processing circuitryof a radio access network node, causes the radio access network node toperform a method according to the seventh aspect.

According to a twelfth aspect there is presented a computer programproduct comprising a computer program according to the eleventh aspectand a computer readable storage medium on which the computer program isstored. The computer readable storage medium could be a non-transitorycomputer readable storage medium.

Advantageously this method enables efficient monitoring of the searchspaces by the wireless device, in turn enabling efficient monitoring ofcontrol regions.

Advantageously this method for enabling monitoring of search spacesenables latency to be reduced compared to existing mechanisms formonitoring of control regions. Decoding is enabled to start afterreception by the wireless device of the control symbol and the firstdata symbol, instead of at the end of the entire subframe as in existingmechanisms for monitoring of control regions. This latency gain may bepossible regardless of whether the control data is common ordevice-specific.

It is to be noted that any feature of the first, second, third, fourth,fifth, sixth seventh, eight, ninth, tenth, eleventh and twelfth aspectsmay be applied to any other aspect, wherever appropriate. Likewise, anyadvantage of the first aspect may equally apply to the second, third,fourth, fifth, sixth, seventh, eight, ninth, tenth, eleventh, and/ortwelfth aspect, respectively, and vice versa. Other objectives, featuresand advantages of the enclosed embodiments will be apparent from thefollowing detailed disclosure, from the attached dependent claims aswell as from the drawings.

Generally, all terms used in the claims are to be interpreted accordingto their ordinary meaning in the technical field, unless explicitlydefined otherwise herein. All references to “a/an/the element,apparatus, component, means, step, etc.” are to be interpreted openly asreferring to at least one instance of the element, apparatus, component,means, step, etc., unless explicitly stated otherwise. The steps of anymethod disclosed herein do not have to be performed in the exact orderdisclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concept is now described, by way of example, withreference to the accompanying drawings, on which:

FIG. 1 schematically illustrates a subframe structure according to priorart;

FIG. 2 is a schematic diagram illustrating a communication networkaccording to embodiments;

FIGS. 3 4, 5, and 6 are flowcharts of methods according to embodiments;

FIG. 7 schematically illustrates an OFDM symbol structure according toan embodiment;

FIG. 8 schematically illustrates control regions comprising PDCCHsscheduling data regions, according to an embodiment;

FIG. 9 is a schematic diagram showing functional units of a wirelessdevice according to an embodiment;

FIG. 10 is a schematic diagram showing functional modules of a wirelessdevice according to an embodiment;

FIG. 11 is a schematic diagram showing functional units of a radioaccess network node according to an embodiment;

FIG. 12 is a schematic diagram showing functional modules of a radioaccess network node according to an embodiment; and

FIG. 13 shows one example of a computer program product comprisingcomputer readable storage medium according to an embodiment.

Like numbers refer to like elements throughout the figures. Any step orfeature illustrated by dashed lines should be regarded as optional.

DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter withreference to the accompanying drawings, on which certain embodiments ofthe inventive concept are shown. This inventive concept may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided by way of example so that this disclosure will be thorough andcomplete, and will fully convey the scope of the inventive concept tothose skilled in the art.

FIG. 2 is a schematic diagram illustrating a communications network 100where embodiments presented herein can be applied. The communicationsnetwork 100 comprises a radio access network (as represented by itsradio coverage area 120 in which a radio access network node 300provides network access), a core network 130, and a service network 140.

The radio access network is operatively connected to the core network130 which in turn is operatively connected to the service network 140.The radio access network node 300 thereby enables wireless devices 200to access services and exchange data as provided by the service network140.

Examples of wireless devices 200 include, but are not limited to, mobilestations, mobile phones, handsets, wireless local loop phones, userequipment (UE), smartphones, laptop computers, tablet computers,sensors, actuators, modems, repeaters, and network-equipped Internet ofThings devices. Examples of radio access network nodes 110 include, butare not limited to, radio base stations, base transceiver stations, NodeBs, evolved Node Bs, gNB (in communications networks denoted “new radio”or NR for short), and access points. As the skilled person understands,the communications system 100 may comprise a plurality of radio accessnetwork nodes 110, each providing network access to a plurality ofwireless devices 200. The herein disclosed embodiments are not limitedto any particular number of radio access network nodes 110 or wirelessdevices 200.

For evolving communications systems, it is envisioned that codewords canbe mapped to individual OFDM symbols, or even several codewords per OFDMsymbol. It is noted that codewords and OFDM symbols are not necessarilyexactly aligned, i.e., some codewords may span multiple OFDM symbols.This may enable the wireless device to start decoding as soon as an OFDMsymbol comprising data has been received.

The fifth generation of mobile telecommunications and wirelesstechnology (5G) is not yet fully defined but in an advanced draftingstage within 3GPP. It includes work on 5G (NR) Access Technology. LTEterminology is used in this disclosure in a forward-looking sense, toinclude equivalent 5G entities or functionalities although a differentterm may be specified in 5G. A general description of the agreements on5G New Radio (NR) Access Technology so far is contained in 3GPP TR38.802 V0.3.0 (2016-10), of which a draft version has been published asR1-1610848. Final specifications may be published inter alia in thefuture 3GPP TS 38.2** series.

There are a few issues with the above disclosed existing mechanisms formonitoring of (data and) control regions when considering an evolvedcommunications system, where low latency is important, and wherebeamformed control messaging is used. Furthermore, in an evolvedcommunications system where the wireless devices in some aspects do notknow the system bandwidth it may be unnecessary to have an L1/L2 controlregion spanning the entire, possibly very large bandwidth, when anywireless device only can access a small part of it. For example, theradio access network node may transmit and receive signals over a 100MHz bandwidth and each wireless device may be limited to transmittingand receiving signals over a 40 MHz bandwidth.

The embodiments disclosed herein therefore relate to mechanisms formonitoring search spaces and for enabling monitoring of search spaces.In order to obtain such mechanisms there are provided a wireless device200, a method performed by the wireless device 200, a computer programproduct comprising code, for example in the form of a computer program,that when run on a wireless device 200, causes the wireless device 200to perform the method. In order to obtain such mechanisms there areprovided a radio access network node 300, a method performed by theradio access network node 300, a computer program product comprisingcode, for example in the form of a computer program, that when run on aradio access network node 300, causes the radio access network node 300to perform the method.

At least some of the embodiments disclosed herein relate to thetransmission, reception, and usage of RSs of different types within anOFDM symbol in the downlink (i.e., as transmitted by the radio accessnetwork node and received by the wireless device). The embodiments mayequally be applicable to an OFDM symbol transmitted in sidelink. Forexample, the RSs may be used for demodulation of control channels thatmay be mapped to a control region.

FIGS. 3 and 4 are flowcharts illustrating embodiments as methods formonitoring search spaces. The methods are performed by the wirelessdevice 200. The methods may advantageously be realized by executingcomputer programs 1320 a.

Reference is now made to FIG. 3 illustrating a method for monitoringsearch spaces as performed by the wireless device 200 according to anembodiment.

If both a common control region in a common search space (enablingbeamforming to reach many wireless devices 200) and device-specificregions in device-specific search spaces (enabling beamforming to reacha specific wireless device) are provided in the same OFDM symbol, or atleast begin in the same OFDM symbol, latencies may be controlled orreduced. Hence, the wireless device 200 is configured to perform stepS104:

-   -   S104: The wireless device 200 receives an OFDM symbol in a        downlink slot. At least part of the OFDM symbol is included in a        device-specific search space and in a common search space.

Upon having received the OFDM symbol the wireless device 200 monitorsboth a device-specific search space and a common search space and isthus configured to perform steps S106, S108:

-   -   S106: The wireless device 200 monitors the device-specific        search space for at least one device-specific reference signal.    -   S108: The wireless device 200 monitors the common search space        for at least one non-device-specific reference signal.

In this respect, to monitor the search space for a reference signal isto be interpreted as: to read the search space attempting to recognizethe reference signal, to search for the reference signal in the searchspace, to try to match the reference signal in the search space, to tryto decode a control message transmitted in the search space knowing thatthe reference signal may be present, and/or to try to decode a controlmessage transmitted in the search space assuming the possible presenceof the reference signal.

The method thus allows for transmission of both common anddevice-specific control messages (possibly beamformed differently) inthe same OFDM symbol, enabling immediate decoding to start in the firstOFDM symbol of any scheduled data region (common and/ordevice-specific). For this purpose, reference signals for data arepreferably inserted in the beginning of the data region.

Embodiments relating to further details of monitoring search spaces asperformed by the wireless device 200 will now be disclosed.

There may be different locations of the OFDM symbol in the downlinkslot. According to an embodiment the OFDM symbol is the first time-wiseoccurring OFDM symbol in the downlink slot. Formulated differently, theOFDM symbol is initial in the downlink slot; with respect to time, theOFDM symbol was transmitted before the other symbols. There may bedifferent locations of the device-specific search space. According to anembodiment at least part of the device-specific search space iscomprised in the first OFDM symbol. There may be different locations ofthe common search space. According to an embodiment at least part of thecommon search space is comprised in the first OFDM symbol.

Reference is now made to FIG. 4 illustrating methods for monitoringsearch spaces as performed by the wireless device 200 according tofurther embodiments. It is assumed that steps S104, S106, S108 areperformed as in the above description with reference to FIG. 3, whichtherefore need not be repeated.

The wireless device may be made aware of the different control regions,location and type henceforth. Hence, according to an embodiment thewireless device 200 is configured to perform step S102:

-   -   S102: The wireless device obtains information regarding        frequency location within the OFDM symbol of the device-specific        search space and the common search space.

This information may comprise respective control region location andsize in the frequency domain. The location may be based on cell ID. Forthe device-specific case the information may be device-specific. Thefrequency locations may be conveyed from the radio access network node300 to the wireless device 200 by means of semi-static signaling overradio resource control (RRC) signaling, medium access control (MAC)element signaling, dynamic signaling in a previous PDCCH, or by othermeans. Optionally, the wireless device may obtain the time location ofthe OFDM symbol, e.g., in terms of the position of the symbol.

Each search space, or control region, may be defined as a set ofsubbands. Hence, according to an embodiment, each of the device-specificsearch space and the common search space is contained in a respectivefrequency subband. Each frequency subband may have a bandwidth in theorder of 5 MHz. Different subbands may have different bandwidths. Acommon control subband and a device-specific control subband can therebybe used within (at least) one and the same OFDM symbol.

A set of non-device-specific demodulation reference signals (DMRS) maybe defined for the common subband or common search space, and a set ofdevice-specific DMRS may be defined for the device-specific subband ordevice-specific search space. Hence, according to an embodiment, thedevice-specific search space comprises resources reserved for adevice-specific DMRS, and the common search space comprises resourcesreserved for a non-device-specific DMRS. In this respect, the fact thatthe resources are reserved is to be interpreted as the resources havepredefined (or pre-agreed) positions in the time/frequency grid. Theremaining resource elements in the OFDM symbol that do not carry RSs maybe used for control payload, such as common and/or device-specificPDCCH. Similarly, each subband or search space may comprise resourcesreserved for multiple DMRSs. If a search space comprises multiple searchspace candidates, each candidate may be associated with its own DMRSresources. DMRS resources of different candidates may overlap orpartially overlap, or may alternatively be disjoint.

As disclosed above, at least part of the OFDM symbol is included in adevice-specific search space and in a common search space. An OFDMsymbol may thus contain common and device-specific search spaces. Eachsearch space may comprise one or several control channel candidates,such as PDCCH candidates, search space candidates, or search spacecontrol channel candidates. If a PDCCH is transmitted, it is transmittedon one of the search space PDCCH candidates. If a PDCCH is transmitted,then also a corresponding DMRS may be transmitted. Depending on whichPDCCH is transmitted, there may be two combinations of PDCCH and DMRSsimultaneously, otherwise only one. Alternatively, DMRS may be connectedto a search space or a search space control channel candidate andtransmitted independently of whether PDCCH is transmitted or not.

Hence, according to an embodiment, the wireless device 200 is configuredto perform steps S106 a, S106 b as part of step S106:

-   -   S106 a: The wireless device 200 detects a device-specific PDCCH        message in the device-specific search space.    -   S106 b: The wireless device 200 identifies, from the        device-specific PDCCH message, resource blocks for a        device-specific data region.

According to a further embodiment the wireless device 200 is configuredto perform steps S108 a, S108 b as part of step S108:

-   -   S108 a: The wireless device 200 detects a non-device-specific        PDCCH message in the common search space.    -   S108 b: The wireless device 200 identifies, from the        non-device-specific PDCCH message, resource blocks for a        non-device-specific data region. In this respect, resource        elements not used for DMRS within a subband may be utilized for        control purposes and/or data transmissions. Resource elements        outside the control subbands may be used for data transmissions.

This means that within a same OFDM symbol, the network, via the radioaccess network node, may transmit a PDCCH addressed to multiple wirelessdevices 200 using a first beamforming setting, and may transmit a PDCCHaddressed to a specific wireless device 200 using a second beamformingsetting, different from the first beamforming setting. Preferably, thefirst beamforming setting is relatively wide or at least wider than thesecond beamforming setting. In this connection, a wide setting is oneexpected to have a low degree of spatial or angular selectivity; inline-of-sight conditions, this corresponds to a large beam angle. Thisallows the wireless device 200 to monitor the search space(s) in thecontrol regions for both group messages and individual messages, decodethese PDCCHs as early as is theoretically possible and start decodingdata code words virtually immediately in the addressed data region.

It can even be envisioned that parts of the OFDM symbol not used forcontrol are used for data. The control regions might not occupy allresources in the OFDM symbol, and hence there may be resources left inthe OFDM symbol that may be utilized for e.g. data traffic to at leastone wireless device 200.

FIGS. 5 and 6 are flowcharts illustrating embodiments as methods forenabling monitoring of search spaces. The methods are performed by theradio access network node 300. The methods may advantageously berealized by executing computer programs 1320 b. In these exampleembodiments, the radio access network node 300 transmits an OFDM symbolin downlink, but variations are equally possible where an OFDM symbol istransmitted in sidelink.

Reference is now made to FIG. 5 illustrating a method for enablingmonitoring of search spaces as performed by the radio access networknode 300 according to an embodiment.

As disclosed above, the wireless device 200 in a step S104 receives anOFDM symbol in a downlink slot. It is assumed that the radio accessnetwork node 300 transmits such an OFDM symbol. Hence, the radio accessnetwork node 300 is configured to perform step S204.

S204: The radio access network node 300 transmits an OFDM symbol in adownlink slot. At least part of the OFDM symbol is included in adevice-specific search space and a common search space. Thedevice-specific search space comprises a device-specific referencesignal, and/or the common search space comprises a non-device-specificreference signal.

It is noted for completeness, that at least one of the search spacescomprises a RS if a physical control channel is transmitted in thedownlink slot. If no physical control channel is transmitted, no RS ispresent.

Embodiments relating to further details of enabling monitoring of searchspaces as performed by the radio access network node 300 will now bedisclosed.

Thus, at least one of (a) and (b) in the following holds: (a) thedevice-specific search space comprises a device-specific referencesignal, (b) the common search space comprises a non-device-specificreference signal.

According to an embodiment the device-specific reference signal enablesa specific wireless device 200 or a specific group of wireless devicesto monitor control messages.

According to an embodiment the non-device-specific reference signalenables non-specific wireless devices in a coverage area of the radioaccess network node 300 to monitor control messages.

Reference is now made to FIG. 6 illustrating methods for enablingmonitoring of search spaces as performed by the radio access networknode 300 according to further embodiments. It is assumed that step S204is performed as described above with reference to FIG. 5, so that thisdescription need not be repeated.

As disclosed above, according to an embodiment the wireless device 200obtains location information. Hence, according to an embodiment theradio access network node 300 is configured to perform step S202:

-   -   S202: The radio access network node 300 provides information        regarding frequency within the OFDM symbol of the        device-specific search space and the common search space to a        wireless device 200.

Further embodiments applicable to both the wireless device 200 and theradio access network node 300 will now be disclosed.

FIG. 7 schematically illustrates an OFDM symbol structure 700 comprisingboth device-specific and non-device-specific control regions 710, 720.Respective control regions comprise resources for respective DMRS. Eachcontrol region comprises resource elements (RE) 740, 760 that arereserved for DMRS. Further REs 730, 750 may contain the PDCCH messages.The densities of the DMRS may be different in different control regionsor may be uniform. The density and locations of respective DMRS may beconfigured or be in accordance with a fixed pattern, in dependence ofthe subband. Further, the DMRS may be associated with individual searchspace PDCCH candidates and only be transmitted if a PDCCH is actuallytransmitted. If a DMRS is associated with an individual search spacePDCCH candidate, DMRS resources of different candidates may overlap,partially overlap or may alternatively be disjoint.

The radio access network node may be configured to only send a referencesignal of a certain type if it also sends a PDCCH message of that type.In that way interference levels in the network may be controlled, orkept small. When transmitted, the reference signals may be located inthe vicinity of the sent PDCCH message within the control region.

FIG. 8 illustrates an OFDM symbol structure 800 comprising bothdevice-specific and non-device-specific control regions (PDCCHs) 810,820 identifying the location in time and/or frequency of data regions830, 840. If the code words in one or both of the common oruser-specific (or device-specific) region are arranged for decoding perOFDM symbol, latency may be reduced. In FIG. 8 the two types of controlregions are non-overlapping, but they may alternatively be fully orpartially overlapping.

Hence, according to an embodiment the device-specific search space andthe common search space at least partially overlap. In case the commoncontrol region and the device-specific control region (partially)overlap, the respective reference signals must be distinguishable. Thereare several ways this may be ensured. The allocation may be that RSs (ofa certain type) are only available when a PDCCH (of that type) isactually transmitted. Then preferably the RSs are transmitted only inthe vicinity of the sent PDCCH. Since the radio access network node isaware of what it sends in a given resource, the radio access networknode can ensure that different types of RSs are distinguishable. Thewireless device 200 only has to monitor the overlapping search spacesusing different assumptions concerning the RS type and concerninglocation of candidate message and RSs. RSs can be made distinguishableif they are transmitted in a non-overlapping fashion, in well enoughisolated beams, or using orthogonal or quasi-orthogonal RS sequences.Different RS for the different search spaces may thus enable a device todistinguish between a control message transmitted in a common searchspace and in a device-specific search space, even if the control channeltransmissions would use the same time-frequency resources.

Alternatively, the device-specific search space and the common searchspace are separated (or disjoint). Hence, according to anotherembodiment the device-specific search space and the common search spacedo not overlap. An allocation scheme may be used to ensure that thedevice-specific RSs and the common RSs do not overlap.

Device-specific RSs may have properties or characteristics which aredependent on the wireless device, a wireless device identity, a CellRadio Network Temporary Identifier (CRNTI), wireless devicecapabilities, a configured parameter for the wireless device, or anyother characteristic that may differentiate two or more wireless devicesor may differentiate two or more groups of wireless devices.

Non-device-specific RSs may have properties or characteristics which aredependent on a cell ID, a location in the time or frequency domain, or aparameter configured for a set of wireless devices. A set of wirelessdevices in this sense may comprise those wireless devices which are toreceive the PDCCH in the common search space; the set may in particularcomprise all wireless devices in a cell.

According to embodiments disclosed herein a control region may thus bemonitored by means of so called search spaces, where a search spacedefines the possible locations of a control message. Properties of asearch space may depend on a size of used control resources; forinstance, in LTE the size is given by the aggregation level. If thereare many possible aggregation levels/sizes of mapped control messages,there are many search spaces. This is true for both device-specific andcommon control regions. The embodiments disclosed herein are notdependent on, or limited to, the exact structure of the control regionsor how they are to be monitored.

An illustrative example of a search space consisting of one singlesubband has been used throughout this description, but as understood bya person of ordinary skill in the art, search spaces may have adifferent number of subbands, possibly of different sizes. That is,although the embodiments and examples disclosed herein depict only oneOFDM symbol comprising control messages, it is clear to the skilledperson that there may be one or more than one OFDM symbol comprisingcontrol messages as long as at least one OFDM symbol comprises bothdevice-specific and non-device-specific search spaces.

FIG. 9 schematically illustrates, in terms of a number of functionalunits, the components of a wireless device 200 according to anembodiment. Processing circuitry 210 is provided using any combinationof one or more of a suitable central processing unit (CPU),multiprocessor, microcontroller, digital signal processor (DSP), etc.,capable of executing software instructions stored in a computer programproduct 1310 a (as in FIG. 13), e.g. in the form of a storage medium230. The processing circuitry 210 may further be provided as at leastone application-specific integrated circuit (ASIC), or fieldprogrammable gate array (FPGA).

Particularly, the processing circuitry 210 is configured to cause thewireless device 200 to perform a set of operations, or steps, S102-S108,as disclosed above. For example, the storage medium 230 may store theset of operations, and the processing circuitry 210 may be configured toretrieve the set of operations from the storage medium 230 to cause thewireless device 200 to perform the set of operations. The set ofoperations may be provided as a set of executable instructions.

Thus the processing circuitry 210 is thereby arranged to execute methodsas herein disclosed. The storage medium 230 may also comprise persistentstorage, which, for example, can be any single one or combination ofmagnetic memory, optical memory, solid state memory or even remotelymounted memory. The wireless device 200 may further comprise acommunications interface 220 at least configured for communications witha radio access network node. As such the communications interface 220may comprise one or more transmitters and receivers, comprising analogueand digital components. The processing circuitry 210 controls thegeneral operation of the wireless device 200 e.g. by sending data andcontrol signals to the communications interface 220 and the storagemedium 230, by receiving data and reports from the communicationsinterface 220, and by retrieving data and instructions from the storagemedium 230. Other components, as well as the related functionality, ofthe wireless device 200 are omitted in order not to obscure the conceptspresented herein.

FIG. 10 schematically illustrates, in terms of a number of functionalmodules, the components of a wireless device 200 according to anembodiment. The wireless device 200 of FIG. 10 comprises a number offunctional modules; a receive module 210 b configured to perform stepS104, a monitor module 210 c configured to perform step S106, and amonitor module 210 f configured to perform step S108. The wirelessdevice 200 of FIG. 10 may further comprise a number of optionalfunctional modules, such as any of an obtain module 210 a configured toperform step S102, a detect module 210 d configured to perform step S106a, an identify module 210 e configured to perform step S106 b, a detectmodule 210 g configured to perform step S108 a, and an identify module210 h configured to perform step S108 b.

In general terms, each functional module 210 a-210 h may in oneembodiment be implemented only in hardware or and in another embodimentwith the help of software, i.e., the latter embodiment having computerprogram instructions stored on the storage medium 230 which when run onthe processing circuitry makes the wireless device 200 perform thecorresponding steps mentioned above in conjunction with FIG. 10. Itshould also be mentioned that even though the modules correspond toparts of a computer program, they do not need to be separate modulestherein, but the way in which they are implemented in software isdependent on the programming language used. Preferably, one or more orall functional modules 210 a-210 h may be implemented by the processingcircuitry 210, possibly in cooperation with the communications interface220 and/or the storage medium 230. The processing circuitry 210 may thusbe configured to from the storage medium 230 fetch instructions asprovided by a functional module 210 a-210 h and to execute theseinstructions, thereby performing any steps as disclosed herein.

FIG. 11 schematically illustrates, in terms of a number of functionalunits, the components of a radio access network node 300 according to anembodiment. Processing circuitry 310 is provided using any combinationof one or more of a suitable central processing unit (CPU),multiprocessor, microcontroller, digital signal processor (DSP), etc.,capable of executing software instructions stored in a computer programproduct 1310 b (as in FIG. 13), e.g. in the form of a storage medium330. The processing circuitry 310 may further be provided as at leastone application-specific integrated circuit (ASIC), or fieldprogrammable gate array (FPGA).

Particularly, the processing circuitry 310 is configured to cause theradio access network node 300 to perform a set of operations, or steps,S202-S204, as disclosed above. For example, the storage medium 330 maystore the set of operations, and the processing circuitry 310 may beconfigured to retrieve the set of operations from the storage medium 330to cause the radio access network node 300 to perform the set ofoperations. The set of operations may be provided as a set of executableinstructions. Thus the processing circuitry 310 is thereby arranged toexecute methods as herein disclosed.

The storage medium 330 may also comprise persistent storage, which, forexample, can be any single one or combination of magnetic memory,optical memory, solid state memory or even remotely mounted memory.

The radio access network node 300 may further comprise a communicationsinterface 320 for communications with other entities and devices of thecommunications network 100 and the wireless device 200. As such thecommunications interface 320 may comprise one or more transmitters andreceivers, comprising analog and digital components.

The processing circuitry 310 controls the general operation of the radioaccess network node 300 e.g. by sending data and control signals to thecommunications interface 320 and the storage medium 330, by receivingdata and reports from the communications interface 320, and byretrieving data and instructions from the storage medium 330. Othercomponents, as well as the related functionality, of the radio accessnetwork node 300 are omitted in order not to obscure the conceptspresented herein.

FIG. 12 schematically illustrates, in terms of a number of functionalmodules, the components of a radio access network node 300 according toan embodiment. The radio access network node 300 of FIG. 12 comprises atransmit module 310 b configured to perform step S204. The radio accessnetwork node 300 of FIG. 12 may further comprise a number of optionalfunctional modules, such as a provide module 310 a configured to performstep S202. In general terms, each functional module 310 a-310 b may beimplemented in hardware or in software. Preferably, one or more or allfunctional modules 310 a-310 b may be implemented by the processingcircuitry 310, possibly in cooperation with the communications interface320 and/or the storage medium 330. The processing circuitry 310 may thusbe arranged to from the storage medium 330 fetch instructions asprovided by a functional module 310 a-310 b and to execute theseinstructions, thereby performing any steps of the radio access networknode 300 as disclosed herein.

FIG. 13 shows one example of a computer program product 1310 a, 1310 bcomprising computer readable means 1330. On this computer readable means1330, a computer program 1320 a can be stored, which computer program1320 a can cause the processing circuitry 210 and thereto operativelycoupled entities and devices, such as the communications interface 220and the storage medium 230, to execute methods according to embodimentsdescribed herein. The computer program 1320 a and/or computer programproduct 1310 a may thus provide means for performing any steps of thewireless device 200 as herein disclosed. On this computer readable means1330, a computer program 1320 b can be stored, which computer program1320 b can cause the processing circuitry 310 and thereto operativelycoupled entities and devices, such as the communications interface 320and the storage medium 330, to execute methods according to embodimentsdescribed herein. The computer program 1320 b and/or computer programproduct 1310 b may thus provide means for performing any steps of theradio access network node 300 as herein disclosed.

In the example of FIG. 13, the computer program product 1310 a, 1310 bis illustrated as an optical disc, such as a CD (compact disc) or a DVD(digital versatile disc) or a Blu-Ray disc. The computer program product1310 a, 1310 b could also be embodied as a memory, such as a randomaccess memory (RAM), a read-only memory (ROM), an erasable programmableread-only memory (EPROM), or an electrically erasable programmableread-only memory (EEPROM) and more particularly as a non-volatilestorage medium of a device in an external memory such as a USB(Universal Serial Bus) memory or a Flash memory, such as a compact Flashmemory. Thus, while the computer program 1320 a, 1320 b is hereschematically shown as a track on the depicted optical disk, thecomputer program 1320 a, 1320 b can be stored in any way which issuitable for the computer program product 1310 a, 1310 b.

The inventive concept has mainly been described above with reference toa few embodiments. However, as is readily appreciated by a personskilled in the art, other embodiments than the ones disclosed above areequally possible within the scope of the inventive concept, as definedby the appended patent claims.

1. A method for monitoring search spaces, the method being performed bya wireless device, the method comprising: receiving an orthogonalfrequency-division multiplexing (OFDM) symbol in a downlink slot,wherein part of the OFDM symbol is included in a device-specific searchspace and part of the OFDM symbol is included in a common search space;monitoring the OFDM symbol for at least one device-specific referencesignal in the device-specific search space and for at least onenon-device-specific reference signal in the common search space.
 2. Themethod of claim 1, further comprising: detecting a device-specificphysical downlink control channel (PDCCH) message in the device-specificsearch space; and identifying, from the device-specific PDCCH message,resource blocks for a device-specific data region.
 3. The method ofclaim 1, further comprising: detecting a non-device-specific physicaldownlink control channel (PDCCH) message in the common search space;identifying, from the non-device-specific PDCCH message, resource blocksfor a non-device-specific data region.
 4. The method of claim 1, whereineach of the device-specific search space and the common search space iscontained in a respective frequency subband.
 5. The method of claim 1,wherein the OFDM symbol is an initial OFDM symbol in the downlink slot.6. The method of claim 1, wherein the device-specific search spacecomprises resources reserved for a device-specific demodulationreference signal (DMRS), and wherein the common search space comprisesresources reserved for a non-device-specific DMRS.
 7. The method ofclaim 1, wherein the non-device-specific DMRS depends on cellparameters, and wherein the device-specific DMRS depends on at least oneparameter of the wireless device.
 8. The method of claim 1, wherein thedevice-specific search space and the common search space at leastpartially overlap.
 9. The method of claim 1, wherein the device-specificsearch space and the common search space are mutually disjoint.
 10. Themethod of claim 1, further comprising: obtaining information regardingfrequency location within the OFDM symbol of the device-specific searchspace and the common search space.
 11. A wireless device for monitoringsearch spaces, the wireless device comprising: processing circuitry; acommunication interface operatively connected to the processingcircuitry; and a storage medium operatively connected to the processingcircuitry and storing instructions that, when executed by the processingcircuitry, cause the wireless device to: receive an orthogonalfrequency-division multiplexing (OFDM) symbol in a downlink slot usingthe communication interface, wherein part of the OFDM symbol is includedin a device-specific search space and part of the OFDM symbol isincluded in a common search space; monitor the OFDM symbol for at leastone device-specific reference signal in the device-specific search spaceand for at least one non-device-specific reference signal in the commonsearch space.
 12. A non-transitory computer-readable medium comprising,stored thereupon, a computer program for monitoring search spaces, thecomputer program comprising computer code configured so that, when thecomputer code is run on processing circuitry of a wireless device, thecomputer code causes the wireless device to: receive an orthogonalfrequency-division multiplexing (OFDM) symbol in a downlink slot usingthe communication interface, wherein part of the OFDM symbol is includedin a device-specific search space and part of the OFDM symbol isincluded in a common search space; monitor the OFDM symbol for at leastone device-specific reference signal in the device-specific search spaceand for at least one non-device-specific reference signal in the commonsearch space.
 13. A method for enabling monitoring of search spaces, themethod being performed by a radio access network node, the methodcomprising: transmitting an orthogonal frequency-division multiplexing(OFDM) symbol in a downlink slot, wherein part of the OFDM symbol isincluded in a device-specific search space and part of the OFDM symbolis included in a common search space, wherein the OFDM symbol comprisesa device-specific reference signal in the device-specific search spaceand/or comprises a non-device-specific reference signal in the commonsearch space.
 14. The method of claim 13, wherein the device-specificreference signal enables a specific wireless device or a specific groupof wireless devices to monitor control messages.
 15. The method of claim13, wherein the non-device-specific reference signal enablesnon-specific wireless devices in a coverage area of the radio accessnetwork node to monitor control messages.
 16. The method of claim 13,further comprising: providing information regarding frequency locationwithin the OFDM symbol of the device-specific search space and thecommon search space to a wireless device.
 17. The method of claim 13,wherein the non-device-specific reference signal depends on cellparameters, and wherein the device-specific reference signal depends onat least one parameter of the wireless device.
 18. A radio accessnetwork node for enabling monitoring of search spaces, the radio accessnetwork node comprising: processing circuitry; a communication interfaceoperatively connected to the processing circuitry; and a storage mediumoperatively connected to the processing circuitry and storinginstructions that, when executed by the processing circuitry, cause theradio access network node to: transmit an orthogonal frequency-divisionmultiplexing (OFDM) symbol in a downlink slot, wherein part of the OFDMsymbol is included in a device-specific search space and part of theOFDM symbol is included in a common search space; wherein the OFDMsymbol comprises a device-specific reference signal in thedevice-specific search space and/or comprises a non-device-specificreference signal in the common search space.
 19. A non-transitorycomputer-readable medium comprising, stored thereupon, a computerprogram for enabling monitoring of search spaces, the computer programcomprising computer code configured so that, when the computer code isrun on processing circuitry of a radio access network node, the computercode causes the radio access network node to: transmit an orthogonalfrequency-division multiplexing (OFDM) symbol in a downlink slot,wherein part of the OFDM symbol is included in a device-specific searchspace and part of the OFDM symbol is included in a common search space;wherein the OFDM symbol comprises a device-specific reference signal inthe device-specific search space and/or comprises a non-device-specificreference signal in the common search space.